A nonvolatile memory can include an array of memory cells. Each of the memory cells can have multiple resistive states. Certain nonvolatile memories (referred to herein as “resistive memories”), such as phase change random access memory (PRAM), resistive random access memory (RRAM), and magnetic random access memory (MRAM), include memory cells with respective resistances. Each of the resistances changes based on the state of the corresponding memory cell. For example, a memory cell can have a first (or low) resistive state when storing a ‘0’ and a second (or high) resistive state when storing a ‘1’.
As a first example, in order to determine a resistive state of a memory cell, a voltage can be applied across the resistance of the memory cell. Current through the resistance may then be detected and is indicative of the resistive state. Based on the detected current, the resistive state of the memory cell is determined. As another example, current can be supplied to the resistance of the memory cell. A voltage across the resistance can then be detected and is indicative of the resistive state. The resistive state of the memory cell can then be determined based on the detected voltage.
Sense amplifiers are used to detect voltages across and/or currents through resistances of memory cells. Sense amplifiers have manufacturing variations and as a result exhibit respective random offset voltage variations. An offset voltage of a sense amplifier refers to differences in voltages of transistors in the sense amplifier. An offset voltage can also change and/or become larger over time and/or cycled use of a sense amplifier.
The larger an offset voltage of a sense amplifier, the lower the overall sensitivity of the sense amplifier to changes in a resistance of a memory cell. A sense amplifier with an offset voltage that is greater than a predetermined threshold can provide an output error. For example, a sense amplifier with an offset voltage that is greater than the predetermined threshold may provide a ‘1’ when a state of a corresponding resistance of a memory cell is actually indicative of a ‘0’ or vice versa. A sense amplifier with an offset voltage that is greater than the predetermined threshold may be referred to as a failed sense amplifier. The output of a failed sense amplifier may be referred to as a failure.